Portable computing devices, for example Portable Navigation Devices (PNDs) that include GPS (Global Positioning System) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems.
In general terms, a modern PND comprises a processor, memory (at least one of volatile and non-volatile, and commonly both), and map data stored within said memory. The processor and memory cooperate to provide an execution environment in which a software operating system may be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the PND to be controlled, and to provide various other functions.
Typically these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include a visual display and a speaker for audible output. Illustrative examples of input interfaces include one or more physical buttons to control on/off operation or other features of the device (which buttons need not necessarily be on the device itself but could be on a steering wheel if the device is built into a vehicle), and a microphone for detecting user speech. In one particular arrangement, the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) additionally to provide an input interface by means of which a user can operate the device by touch.
Devices of this type will also often include one or more physical connector interfaces by means of which power and optionally data signals can be transmitted to and received from the device, and optionally one or more wireless transmitters/receivers to allow communication over cellular telecommunications and other signal and data networks, for example Bluetooth, Wi-Fi, Wi-Max, GSM, UMTS and the like.
PNDs of this type also include a GPS antenna by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device.
The PND may also include electronic gyroscopes and accelerometers which produce signals that can be processed to determine the current angular and linear acceleration, and in turn, and in conjunction with location information derived from the GPS signal, velocity and relative displacement of the device and thus the vehicle in which it is mounted. Typically, such features are most commonly provided in in-vehicle navigation systems, but may also be provided in PNDs if it is expedient to do so.
The utility of such PNDs is manifested primarily in their ability to determine a route between a first location (typically a start or current location) and a second location (typically a destination). These locations can be input by a user of the device, by any of a wide variety of different methods, for example by postcode, street name and house number, previously stored “well known” destinations (such as famous locations, municipal locations (such as sports grounds or swimming baths) or other points of interest), and favourite or recently visited destinations.
Typically, the PND is enabled by software for computing a “best” or “optimum” route between the start and destination address locations from the map data. A “best” or “optimum” route is determined on the basis of predetermined criteria and need not necessarily be the fastest or shortest route. The selection of the route along which to guide the driver can be very sophisticated, and the selected route may take into account existing, predicted and dynamically and/or wirelessly received traffic and road information, historical information about road speeds, and the driver's own preferences for the factors determining road choice (for example the driver may specify that the route should not include motorways or toll roads).
In addition, the device may continually monitor road and traffic conditions, and offer to or choose to change the route over which the remainder of the journey is to be made due to changed conditions. Real time traffic monitoring systems, based on various technologies (e.g. mobile phone data exchanges, fixed cameras, GPS fleet tracking) are being used to identify traffic delays and to feed the information into notification systems.
PNDs of this type may typically be mounted on the dashboard or windscreen of a vehicle, but may also be formed as part of an on-board computer of the vehicle radio or indeed as part of the control system of the vehicle itself. The navigation device may also be part of a hand-held system, such as a PDA (Portable Digital Assistant), a media player, a mobile phone or the like, and in these cases, the normal functionality of the hand-held system is extended by means of the installation of software on the device to perform both route calculation and navigation along a calculated route.
Route planning and navigation functionality may also be provided by a desktop or mobile computing resource running appropriate software. For example, the Royal Automobile Club (RAC) provides an on-line route planning and navigation facility at http://www.rac.co.uk, which facility allows a user to enter a start point and a destination whereupon the server with which the user's computing resource is communicating calculates a route (aspects of which may be user specified), generates a map, and generates a set of exhaustive navigation instructions for guiding the user from the selected start point to the selected destination. The facility also provides for pseudo three-dimensional rendering of a calculated route, and route preview functionality which simulates a user travelling along the route and thereby provides the user with a preview of the calculated route.
In the context of a PND, once a route has been calculated, the user interacts with the navigation device to select the desired calculated route, optionally from a list of proposed routes. Optionally, the user may intervene in, or guide the route selection process, for example by specifying that certain routes, roads, locations or criteria are to be avoided or are mandatory for a particular journey. The route calculation aspect of the PND forms one primary function, and navigation along such a route is another primary function.
During navigation along a calculated route, it is usual for such PNDs to provide visual and/or audible instructions to guide the user along a chosen route to the end of that route, i.e. the desired destination. It is also usual for PNDs to display map information on-screen during the navigation, such information regularly being updated on-screen so that the map information displayed is representative of the current location of the device, and thus of the user or user's vehicle if the device is being used for in-vehicle navigation.
An icon displayed on-screen typically denotes the current device location, and is centred with the map information of current and surrounding roads in the vicinity of the current device location and other map features also being displayed. Additionally, navigation information may be displayed, optionally in a status bar above, below or to one side of the displayed map information, examples of navigation information include a distance to the next deviation from the current road required to be taken by the user, the nature of that deviation possibly being represented by a further icon suggestive of the particular type of deviation, for example a left or right turn. The navigation function also determines the content, duration and timing of audible instructions by means of which the user can be guided along the route. As can be appreciated a simple instruction such as “turn left in 100 m” requires significant processing and analysis. As previously mentioned, user interaction with the device may be by a touch screen, or additionally or alternately by steering column mounted remote control, by voice activation or by any other suitable method.
A further important function provided by the device is automatic route re-calculation in the event that: a user deviates from the previously calculated route during navigation (either by accident or intentionally); real-time traffic conditions dictate that an alternative route would be more expedient and the device is suitably enabled to recognize such conditions automatically, or if a user actively causes the device to perform route re-calculation for any reason.
It is also known to allow a route to be calculated with user defined criteria; for example, the user may prefer a scenic route to be calculated by the device, or may wish to avoid any roads on which traffic congestion is likely, expected or currently prevailing. The device software would then calculate various routes and weigh more favourably those that include along their route the highest number of points of interest (known as POIs) tagged as being for example of scenic beauty, or, using stored information indicative of prevailing traffic conditions on particular roads, order the calculated routes in terms of a level of likely congestion or delay on account thereof. Other POI-based and traffic information-based route calculation and navigation criteria are also possible.
Although the route calculation and navigation functions are fundamental to the overall utility of PNDs, it is possible to use the device purely for information display, or “free-driving”, in which only map information relevant to the current device location is displayed, and in which no route has been calculated and no navigation is currently being performed by the device. Such a mode of operation is often applicable when the user already knows the route along which it is desired to travel and does not require navigation assistance.
Devices of the type described above, for example, the 720T model manufactured and supplied by TomTom International B.V., provide a reliable means for enabling users to navigate from one position to another. Such devices are of great utility when the user is not familiar with the route to the destination to which they are navigating.
In order to facilitate in-vehicle use of the PND, some PNDs are equipped with a Frequency Modulation (FM) transmitter, for example the 920T model PND available from TomTom International B.V. Instead of amplified audio signals being reproduced by a loudspeaker of the PND, the FM transmitter frequency modulates and transmits the audio signals on a user-selectable frequency. When in a vehicle, a user of the PND tunes an FM radio located in the vehicle to the user-selected frequency so that the FM radio receives the frequency modulated audio signal, demodulates the frequency modulated audio signal and reproduces the audio signal through loudspeakers coupled to the FM radio. Of course, the FM radio can be part of an in-vehicle entertainment system capable of FM reception and including a Compact Disc (CD) multi-changer and other facilities.
It should be noted that it is desirable to use the loudspeakers of in-vehicle entertainment systems via FM transmission for other types of portable device, for example so-called MP3 players and/or mobile telephones. Indeed, it is known for such other portable devices to possess so-called Short-Range Radio (SRR) FM transmitters to transmit audio to FM receivers.
More recently, it has been discovered that advantage can be taken of Radio Data System (RDS) capabilities possessed by many in-vehicle entertainment systems, for example RDS FM radio receivers. On an available channel, a portable device equipped with an RDS encoder transmits, inter alia, a Programme Identification (PI) code, a Programme Service (PS) name (for example, “TomTom”) and a list of Alternative Frequencies (AF), the available channel and the list of AFs being selected from free channels detected amongst an FM “landscape” of channels in which the portable device is operating. The formation and transmission of the PI code, the PS name and the list of AFs are in accordance with the RDS technical specification set out by the International Electrotechnical Commission (IEC). The portable device also typically transmits an audio test message on the same available channel.
The user sets an FM radio to scan for the FM transmission from the portable device and identified by the RDS information transmitted by the portable device. When the transmission by the portable device has been found by the FM radio, the frequency modulated audio signal transmitted by the portable device, typically the audio test message, is reproduced by the loudspeakers of the FM radio and a display of the FM radio displays the PS name, namely “TomTom” in this example.
However, in order to operate in accordance with the RDS technical specification, the RDS encoder of the portable device has to transmit, using RDS terminology, a group comprising a unique PI code, which is not in use by regular broadcasters in a geographic area in which the portable device is being operated. If the PI code used is not unique, the FM radio is likely to identify a regular transmitter employing the same PI code instead of the desired SRR FM transmitter of the portable device. In circumstances where the regular transmitter has national coverage, it will be necessary to re-tune the FM radio to the transmission of the portable device on an alternative frequency, but this is likely to be confusing for the average user due to a limited working knowledge of the RDS.
According to the RDS technical specification, the PI code is formed from a series of 4 nibbles, a first nibble comprising a so-called Country Code (CC), a second nibble being used to indicate coverage area of a service, and a third nibble and a fourth nibble are reserved for a programme identification number. As a result of discussions between manufacturers of RDS Integrated Circuits (ICs) and the RDS Forum, it was initially concluded that a PI code should be allocated for use by portable devices, the PI code having a CC of 0 in order to avoid conflicts with other PI codes being used at a national level for radio broadcasts. However, the CC of 0 is excluded by the RDS technical specification and some RDS-equipped receivers may be programmed not to recognise the use of the CC of 0 due to the exclusion. Instead, an alternative proposal is to allow the first nibble of the PI code, i.e. the CC, to be set to a value between 1 and F (hexadecimal), and to set the third and fourth nibbles to 0. The second nibble is set to 0 to 1, depending upon whether or not the SRR transmitter is capable of implementing AFs. In practice, where AFs are contemplated, this structure only accommodates 15 practical codes, namely: 1100, 2100, 3100, 4100, . . . , C100, D100, E100, F100. Assuming that, on average, the FM landscape of channels comprises 3 available FM channels, the likelihood of mutual interference between portable devices is about 17% and interference between SRR transmitters with the same PI code, for example PNDs waiting at traffic lights, is about 1%. Whilst this latter percentage may seem small, it is nevertheless significant. In this respect, in the example of two PNDs waiting at traffic lights, the interference can result in the loudspeaker of an FM radio in one vehicle reproducing audible navigation instructions from another PND located in a neighbouring vehicle. The consequences of such interference can result in substantial inconvenience to the recipient of the wrong navigation instructions. In the more general case of portable devices, interference experienced by a driver from an MP3 player located in a nearby vehicle can be inconvenient and undesirable as it constitutes an unwanted interruption to enjoyment of other media.